Recently, as electronic equipments are downsized and lightened and use of portable electronic instruments is generalized, research and development into lithium secondary batteries have been made intensively. Lithium secondary batteries are generally obtained by using materials capable of lithium ion intercalation/deintercalation as anode and cathode and filling an organic electrolyte or polymer electrolyte into the gap between the cathode and anode. Such lithium secondary batteries generate electric energy by redox reactions when lithium ion intercalates or deintercalates at the cathode and anode.
Because a lithium secondary battery serves to transfer energy while lithium ions reciprocate between a cathode and anode like a rocking chair, it is also referred to as a “rocking chair battery”. During the first charge cycle, an anode active material such as the surface of carbon particles is reacted with an electrolyte to form a solid electrolyte interface (SEI) film at an anode. The SEI film serves to inhibit decomposition of the electrolyte on the surface of anode active material and thus to stabilize a battery. However, because a certain amount of lithium is consumed in order to form the SEI film, amount of reversible lithium decreases, followed by degradation in the battery capacity. Particularly, when irreversible capacity of an anode is large in a currently used secondary battery system whose lithium source is present at a cathode, irreversibility of the anode results in a dead volume of the cathode. Therefore, in practice, the cathode provides a capacity lower than the actual capacity applicable to the cathode, resulting in degradation in the battery capacity.